bogs in second gear

[jcs327]

I just drilled the airbox on my all stock 400ex. I noticed that when I come off the line in second, it bogs before picking up and going. I lowered the clip on the needle one notch, but it did not change. I am still running the stock filter, but I am soon going to a K&N. What should I do to get rid of the bog? Go to a 152 main jet? Thanks in advance.

[AtvMxRider]

You need to rejet cause you are running lean.

[AtvMxRider]

Oh yeah welcome to the site:) .

[1fast400ex]

could you come out in 2nd before u drilled the holes

[jcs327]

do you think a 152 will do the trick?

[AtvMxRider]

Originally posted by jcs327
do you think a 152 will do the trick?

it's a start. Nobody can tell ya exactly what your jetting will be caus eit's more of a trial and error. But a 152 might do it for ya.

[jcs327]

it bogged before I drilled the box. I figured drilling the box would help, and it did a little. I noticed the plug was a little white, so I moved the needle clip down one notch. Once the rpm's pick up, it rocks. Its just taking off in second that bogs it.

[1fast400ex]

why not just go with a 14 tooth front sprocket and forget jetting theres no need to rejet for holes in the lid or even with a k&n. that is if your wanting to come out in second easily

[AtvMxRider]

Originally posted by 1fast400ex
why not just go with a 14 tooth front sprocket and forget jetting theres no need to rejet for holes in the lid or even with a k&n. that is if your wanting to come out in second easily


Your increasing the air flow into the engine. Why wouldn't you rejet?:huh

[1fast400ex]

with just drilling air holes your not letting that much more air in try taking the lid off and checking the plug u wont notice much difference. he stated that he was still running the stock pipe and stock filter. without a pipe he not going to get the air out. all i was saying is he can gain alot more bottom without rejetting.

[cals400ex]

i would put in a 150. i think a 152 would make it a little rich. you won't notice many gains by just drilling holes in the lid. good luck

[jcs327]

thanks. I think I am going to install a fmf powercore IV with a 152 jet & see what that does.

[jcs327]

I put in a 155 main jet and moved the needle clip down 1 notch.
From 1/2 to full throttle it's eye watering fast, but it still bogs at first when I come out of the hole in second gear. Do I need to go up on the pilot jet? The plug is light tan now.

[cals400ex]

light tan is a good color. i would recommend putting in a 42 pilot jet anyways. if the bike felt like it was bogging before you did anything to the bike, i bet your just use to the power band of the 400ex and you are now ready for more. are you running stock gearing and tires? maybe you need to use the clutch a little more when coming out of a corner too. second won't have tons of torque at slow speeds on a stock bike.

[jcs327]

I am still running stock gearing. I noticed a big gain on the top end after the 155 main was installed. I am hoping that the pipe will do the trick for the low end.

[bmw500hp]

Originally posted by jcs327
I am still running stock gearing. I noticed a big gain on the top end after the 155 main was installed. I am hoping that the pipe will do the trick for the low end.

JCS, Have you ever been cruising or creeping in first or second. Suddenly pinned the throttle and experienced the same problem?:confused:

[jcs327]

No, I have good power when I am going slow and hammer it. It is only on take-off from second in a dead stop that it bogs from idle to about 1/4 throttle, then the rpm's pick up and it hammers.

[bmw500hp]

Originally posted by jcs327
No, I have good power when I am going slow and hammer it. It is only on take-off from second in a dead stop that it bogs from idle to about 1/4 throttle, then the rpm's pick up and it hammers.

On my new build, airbox on..... I have relatively the same symptoms. Revs need to build a bit before the pull.

Airbox off......abolutely perfect, pulls and Rips! no hesitation. I am absolutely stunned at the difference. Night and Day. The bike pulls strong right out of a low rev bog!

(6) one inch holes drilled in a spare airbox lid.... Hardly better than with the lid on.

Now I am talking about when the quad is lugged in second and I hammer it pull out.

[whitebrothers]

I think you might be riding it wrong you will bog if you dont get the rpms up for the start, also try to take the spark arrester out it will sound better and go a little bit faster,(not noticebly) also if it is stock you should realy only have to go up one on the main jet.

I think you not pining the gas on the start but thats me.
hope it works out:D

[MOFO]

Originally posted by jcs327
from idle to about 1/4 throttle, then the rpm's pick up and it hammers.


Right here is your problem. Your main jet doesnt do much in this throttle range. Your pilot jet and needle control this area....

Think of it like this...very rough scale.

idle - 1/4 throttle is your pilot
1/4 - 3/4 throttle is your needle
1/3 - wide open is your main jet

Note: all of these ranges do overlap each other...its not a fine cut off.

You also have to factor in your air mixture screw which plays a part in all areas.

From what you have described, I would move your clip on your needle one slot and bump up to a 40-42 pilot jet. I would also consider a 14 tooth front sprocket if you want a good take off in 2nd gear.